🚀 go-pugleaf

Note that "{" got lost somewhere, I'm assuming they are where they
need to be.

The key problem is that you created an object of class array of B with
space for 5 elements. That means you can put references to B in it, or
references to objects of any class derived, directly or indirectly,
from B. You cannot put an A reference in it, because A is a superclass
of B, not a subclass.

A is a superclass of B, so any array of B references can only contain
references that could also be in an array of A references. It is O.K.
to use a variable of type A[] to refer to an object of class B[], but
like any object its class does not change.

If you want the array to contain a mixture of references to A and to
B, instantiate it as a A[5], not B[5].

Patricia


Shashank wrote:
> 
> Consider the following Java Program
> 
> class A
> 
>     int id;
>     A()
> 
>        id = 1;
>     }
>     A(int i)
> 
>        id = i;
>     }
>     public int id()
> 
>        return id;
>     }
> }
> class B extends A
> 
>     B(int i)
> 
>     }
> }
> public class FinalC
> 
>     public static void main(String[] args)
> 
>        A[] array = new B[5];
>        array[0] = new B(10);
>        array[1] = new B(8);
>        array[2] = new B(6);
>        array[3] = new A(4); // line 23
>        array[4] = new A(2); // line 24
>        for(int i = 0; i< 5; i++)
> 
>           System.out.println(array[i].id());
>        }
>     }
> }
> 
> The execution returns the exception:
> 
> java.lang.ArrayStoreException:
>         at FinalC.main(FinalC.java:23)
> 
> Why the program runs in this way.
> What Changes should I make to the instructions on lines 23 and 24 to correct
> the problem.

Shashank schrieb in Nachricht <7olh27$sb$1@news.chorus.net>...
>Consider the following Java Program


>class A
...
>class B extends A
...

>       A[] array = new B[5];
>       array[0] = new B(10);
>       array[1] = new B(8);
>       array[2] = new B(6);
>       array[3] = new A(4); // line 23
>       array[4] = new A(2); // line 24
>       for(int i = 0; i< 5; i++)

...
>java.lang.ArrayStoreException:
>        at FinalC.main(FinalC.java:23)


the error is some lines above.

A[] array = new B[5];

you have a declared A-array, but it is implemented as an B-array. So only B
and subclasses of B are allowed. On the other hand, you get only A-objects
out of this array.

A[] array = new A[5];
this helps, now you can insert A-objects and get-out A-objects.

To understand this behavior, you should remember that array's are just
special objects.

Ciao, Alex